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NAME="CATALOG-PG-LARGEOBJECT"
>45.28. <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
></A
></H1
><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
> holds the data making up
   <SPAN
CLASS="QUOTE"
>"large objects"</SPAN
>.  A large object is identified by an OID
   assigned when it is created.  Each large object is broken into
   segments or <SPAN
CLASS="QUOTE"
>"pages"</SPAN
> small enough to be conveniently stored as rows
   in <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
>.
   The amount of data per page is defined to be <TT
CLASS="SYMBOL"
>LOBLKSIZE</TT
> (which is currently
   <TT
CLASS="LITERAL"
>BLCKSZ/4</TT
>, or typically 2 kB).
  </P
><P
>   Prior to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.0, there was no permission structure
   associated with large objects.  As a result,
   <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
> was publicly readable and could be
   used to obtain the OIDs (and contents) of all large objects in the system.
   This is no longer the case; use
   <A
HREF="catalog-pg-largeobject-metadata.html"
><TT
CLASS="STRUCTNAME"
>pg_largeobject_metadata</TT
></A
>
   to obtain a list of large object OIDs.
  </P
><DIV
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><P
><B
>Table 45-28. <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
> Columns</B
></P
><TABLE
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><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>loid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-largeobject-metadata.html"
><TT
CLASS="STRUCTNAME"
>pg_largeobject_metadata</TT
></A
>.oid</TT
></TD
><TD
>Identifier of the large object that includes this page</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>pageno</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>Page number of this page within its large object
      (counting from zero)</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>data</TT
></TD
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Actual data stored in the large object.
       This will never be more than <TT
CLASS="SYMBOL"
>LOBLKSIZE</TT
> bytes and might be less.
      </TD
></TR
></TBODY
></TABLE
></DIV
><P
>   Each row of <TT
CLASS="STRUCTNAME"
>pg_largeobject</TT
> holds data
   for one page of a large object, beginning at
   byte offset (<TT
CLASS="LITERAL"
>pageno * LOBLKSIZE</TT
>) within the object.  The implementation
   allows sparse storage: pages might be missing, and might be shorter than
   <TT
CLASS="LITERAL"
>LOBLKSIZE</TT
> bytes even if they are not the last page of the object.
   Missing regions within a large object read as zeroes.
  </P
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